Exclusive Video: Newark Emergency Plane Landing

Arlene Salac, a spokeswoman for the Federal Aviation Administration, said the Airbus 319's right main landing gear did not extend, although its nose and left main landing gear did, making for a bumpier-than-usual landing. United Airlines spokeswoman Robin Urbanski said it was not clear what caused the malfunction.

Passengers tell NBCNewYork that the flight had to dump fuel before it touched down. Passengers were forced to vacate the plane down emergency chutes that were deployed upon landing.

Marc Greenstein, who works for MSNBC, was on the flight at the time. He said the right rear landing gear did not deploy. Photos and video he captured after getting off the plane show its emergency escape chutes deployed, and police and fire trucks surrounding the aircraft. Emergency personnel usher passengers away from the plane, but not before one woman stops to hug and thank a man for helping her get off the plane.

The flight was eventually expected to return to Chicago and then on to Oregon. The incident caused some delays at Newark on Sunday.

Passengers said the pilot and crew skillfully helped steer the plan through a stressful landing and United Airlines said it is refunding all the passengers the cost of the ticket. The airline will also offer them miles or vouchers, company officials told NBCNewYork.

MaryAlice Breuninger; from Morristown, NJ; was waiting for her brother to arrive on the flight. She said her brother called to say that everything was ok but that some people of the plane had been "pretty shaken up."

"This is the type of waiting you want to do, when you know everything is ok," she said.

Paul Lasiuk from Chicago was on the plane.

"I've had bumpier landings here in Newark... The pilot did a great job," he said.